Exploring T and S parameters in Vector Meson Dominance Models of Strong Electroweak Symmetry Breaking

TL;DR

This paper analyzes electroweak precision constraints in Higgsless strong EWSB models using Vector Meson Dominance, focusing on S and T parameters, resonance couplings, and their implications for model viability.

Contribution

It provides a detailed analysis of S and T parameters in Higgsless models, incorporating one-loop resonance effects and conditions for custodial symmetry preservation.

Findings

Resonance couplings constrained by unitarity and formfactor behavior.

One-loop resonance contributions can improve electroweak fit.

Second Weinberg sum rule does not converge in these models.

Abstract

We revisit the electroweak precision tests for Higgsless models of strong EWSB. We use the Vector Meson Dominance approach and express S and T via couplings characterizing vector and axial spin-1 resonances of the strong sector. These couplings are constrained by the elastic unitarity and by requiring a good UV behavior of various formfactors. We pay particular attention to the one-loop contribution of resonances to T (beyond the chiral log), and to how it can improve the fit. We also make contact with the recent studies of Conformal Technicolor. We explain why the second Weinberg sum rule never converges in these models, and formulate a condition necessary for preserving the custodial symmetry in the IR.